tisdag 1 januari 2013

Negative Climate Sensitivity: Global Cooling 2

Climate sensitivity as the effect on the Earth surface temperature of doubled atmospheric CO2, is by IPCC estimated to an alarming + 3 C. The idea is that CO2 by acting like a "greenhouse gas" blocks radiation from the Earth and thus causes warming. This is a very primitive idea and as such it may well be wrong.

Let us see what basic thermodynamics says:

The Earth surface is heated by incoming energy from the Sun, and the Earth-atmosphere system radiates an equal amount of energy from an outer boundary or top of the atmosphere TOA at the tropopause at a pressure of 0.2 - 0.3 bar.

The surface temperature is determined by the lapse rate from the temperature at TOA.

In an atmosphere without thermodynamics of advection (still air) energy would be transported from the Earth surface to TOA by a combined process of conduction and radiation, which would require a linear temperature profile with constant lapse rate equal to the dry adiabatic lapse rate of 10 C/km as the maximal rate of a stable atmosphere without advective overturning (thus establishing the Loschmidt gravito-thermal effect).

The observed lapse rate in the real atmosphere with thermodynamics of advection is 6.5 C/km.

Increasing thermodynamics would thus tend to decrease the lapse rate and with a temperature of TOA unchanged, would thus cause global cooling.

The logic is that more vigorous thermodynamics would transport energy more efficiently from the Earth surface and thus cause cooling.

Doubled CO2 could increase the temperature of TOA, by decreasing the direct radiation to outer space from the Earth surface, but would also demand a more vigorous thermodynamics reducing the lapse rate.

The rationale is that conduction/radiation passively operates on a temperature gradient/lapse rate maintained by exterior forcing, while thermodynamics/advection actively works to decrease the gradient/lapse rate. To see the active part dominate the passive would not be surprising.

Climate sensitivity would thus come out by subtracting effects of radiation and thermodynamics, and not as suggested by IPCC by adding these effects. This may explain why the +3 C by IPCC is not what is observed, and that what is observed is close to 0 or even negative.